1. Field of the Invention:
The present invention relates to a plasma processing apparatus capable of obtaining a satisfactory plasma arc, smoothly performing the start of the plasma processing with regard to plasma cutting or welding and the like, and a processing method used by this plasma processing apparatus.
2. Description of the Prior Art:
In order to stabilize the start of the plasma processing, hitherto required the use of a large quantity of gas flow, or a larger pressure than a fixed numerical value established by using a high electric current or a high voltage for an electrode of the plasma torch. Alternatively, the plasma processing was started while gas and electricity were controlled by arranging a wrap of a negative electrode between an electrode of the plasma torch and a nozzle. In the customary torch, there are problems. For examples, the life of the electrode and the nozzle are reduced remarkbly by the use of a high electric current or a high voltage, and when setting up a wrap of the negative electrode, the structure of the apparatus becomes complicated, the apparatus is prone to break downs, and the cost becomes expensive.
Also, when plasma processing is carried out by the customary plasma processing apparatus, several conditions may vary to some degree. These conditions include a plasma electric current, plasma gas electric current, a mixing ratio of the plasma gas, a bore of the jetting nozzle for the plasma arc use and the like. Varying conditions will result in a frequency of the plasma electric current varying, and consequently there are problems. For instance, when the plasma arc becomes unsteady, the length of the plasma arc may expand with alignment or retract, which has a bad affect on the processing.